The pantropical spotted dolphin (Stenella attenuata) is a species of dolphin found in all the world's temperate and tropical oceans.[4] The species was beginning to come under threat due to the killing of millions of individuals in tunapurse seines. In the 1980s, the rise of "dolphin-friendly" tuna capture methods saved millions of the species in the eastern Pacific Ocean and it is now one of the most abundant dolphin species in the world.
The species was first described by John Gray in 1846. Gray's initial analysis included the Atlantic spotted dolphin in this species. They are now regarded as separate. Both the genus and specific names come from Latin words meaning thin or thinning.
Two subspecies of the pantropical spotted dolphin are recognized:[5]
S. a. attenuata or offshore pantropical spotted dolphin, found worldwide in tropical waters
S. a. graffmani or coastal pantropical spotted dolphin, found in coastal waters in the eastern tropical Pacific
Another unnamed subspecies, which inhabits inland Hawaiian waters, was recognized in Rice (1998)'s overview of marine mammal taxonomy.[6]
The pantropical spotted dolphin varies significantly in size and coloration throughout its range. The most significant division is between coastal and pelagic varieties. The coastal form is larger and more spotted. (These two forms have been divided into subspecies only in eastern Pacific populations).
Spots are key defining characteristics in adults, though immature individuals are generally uniformly colored[4] and susceptible to confusion with the bottlenose dolphin. Populations around the Gulf of Mexico may be relatively spot-free even in adulthood. In the Atlantic, confusion is possible with the Atlantic spotted dolphin.
The pantropical spotted dolphin is a fairly slender, streamlined animal, with a dark cape and light spots on its body that increase in number and size as it gets older.[4][7][8] This species has a long, thin beak and a falcate dorsal fin, which is the thinnest among dolphins.[7][8] The upper and lower jaws are darkly colored, but are separated by thin, white "lips". The chin, throat, and belly are white to pale grey with a limited number of spots. The flanks are separated into three distinct bands of color— the lightest at the bottom, followed by a thin, grey strip in the middle of the flank, and a dark-grey back. The tall concavedorsal fin is similarly colored. The thick tail stock matches the color of the middle band.
The vocal repertoire of the pantropical spotted dolphin has not been clearly documented. There is no published information about the acoustic signals from South Atlantic Ocean populations of the mammal.[9]
The pantropical spotted dolphin is very active and is prone to making large, splashy leaps from the sea. It is a common breacher and will often clear the water for a second or more. Bow-riding and other play with boats is common.
In the eastern Pacific, the dolphin is often found swimming with yellowfin tuna (hence the problem with dolphin deaths caused by tuna fishing). However, they do not feed on that fish. In fact, the two species have similar diets of small epipelagic fish. In other areas, the species may also feed on squid and crustaceans.
Birth length is 80–90cm. Adults are about 2.5 m long and weigh 110 to 140kg. Sexual maturity is reached at 10 years in females and 12 years in males. The average lifespan is around 40 years.[4]
Population and distribution
The pantropical spotted dolphin, as its name implies, is widely distributed around tropical and marine waters from 40°N and 40°S and is one of the most common dolphin species in the Atlantic and Indian oceans.[7][8] The total world population is in excess of three million— the second-most abundant cetacean after the bottlenose dolphin— of which two million are found in the eastern Pacific. However, this represents a decrease from at least 7 million since the 1950s.
The pantropical spotted dolphin is the most common cetacean species observed within the Agoa Sanctuary, located in the Lesser Antilles in the eastern Caribbean.[7][8] Because it is common within the sanctuary it is considered a resident species; however, no research has been carried out to estimate its population status and movement patterns between islands.[7][8]
Centres of highest population density are the shallow warmest waters (water temperature in excess of 25°C). They also tend to concentrate where a high temperature gradient is found.
The pantropical spotted dolphin's propensity for associating with tuna, particularly in the eastern Pacific, has in recent history been a very real danger. In the 1960s and 1970s, fishermen would capture thousands of dolphin and tuna at once using purse seine nets. The dolphins all died. Over a period of about 25 years, 75% of this region's population, and over half the world's total were wiped out. The issue has received wide public attention. Many major supermarkets have found it economically expedient to use tuna suppliers whose fisherman catch tuna by more discriminatory means, and thus advertise their tuna product as dolphin-friendly. Some such products are approved by the Whale and Dolphin Conservation Trust.[10]
Negative impacts from fishing activities remain, despite broad "dolphin-safe" practices. Instead of reducing numbers through direct mortalities, fishing activities have disrupted the reproductive output of the northeastern pantropical spotted dolphin. The fishing had a negative impact on calf survival rates and/or birth rates. This could be caused when fishing operations separate mothers from their suckling calves, interfere with the conception or gestation of calves, or a combination of the two.[11]
Major threats
The eastern Pacific populations of pantropical spotted dolphins are divided into 3 units – coastal and 2 offshore populations, northeastern and western-southern.[12] Just under 5 million dolphins were killed between 1959 and 1972. 3 million of these were from the northeastern offshore population unit.[13] Since that time, this subpopulation has been the slowest to recover, if it is truly recovering at all.[14] Natural mortalities are occurring as well, but they are difficult to estimate.[15]
The major threat to Stenella attenuata is individuals killed as by-catch in fisheries.[12] Tuna fishermen follow pantropical spotted dolphins in order to find and catch fish. The height of incidental killings was in the 1960s and 1970s.[2] Tuna fishermen from the 1950s to the 1980s in the eastern Pacific killed massive numbers of dolphins, most of which were offshore spotted dolphins.[2]
Another threat to this species is gillnet fisheries in Australia, North Pacific (central and northern areas), Peru, Ecuador, Japan, and Philippines.[2] Trawls in West Africa and long-lining in the Central Atlantic likewise pose significant threats to these species.[12] Small directed catches in other parts of the world are not as well documented. There is a large-mesh pelagic driftnet fishery of eastern Taiwan where a large number of dolphin killings are suspected.[2] The exact number of deaths due to this fishery is unknown.
Japan catches pantropical spotted dolphins for human consumption.[2] The average catch between 1995 and 2004, was 129 animals annually.[16] Pantropical spotted dolphins are the preferred species for consumption in Taiwan.[2]
Conservation actions
The eastern tropical Pacific and Southeast Asian populations of the pantropical spotted dolphin are listed in Appendix II[17] of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). As the pantropical spotted dolphin can be divided into three subspecies, studies of these distinct populations would be needed to assess conservation efforts.[18]
In addition, the pantropical spotted dolphin is covered by the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia (Western African Aquatic Mammals MoU) and the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (Pacific Cetaceans MoU).[19] The U.S. Marine Mammal Protection Act was established in 1972. U.S. Fishing vessels have since reduced dolphin by-catch deaths by 95%.[20] The U.S. Marine Mammal Protection Act lists the northeastern and coastal stocks as “Depleted.”[21]
Dolphin deaths have greatly decreased since the establishment of the Inter-American Tropical Tuna Commission (IATTC). The Commission set mortality limits on the international fleet. In 2005, only 373 spotted dolphin deaths were observed.[22]
Dolphin populations are able to grow at 4% per year,[23] but the pantropical spotted dolphin populations did not improve or worsen between 1979 and 2000.[24] The population has not recovered, even though 30 years of management has been in effect.
Although the US and international fishing agencies have reduced dolphin bycatch significantly, the northeastern subpopulation is not showing strong signs of recovery.[14] This lack of recovery of the subpopulations of the pantropical spotted dolphins could be due to the following reasons: calf separation, orphaning, fishery stress, under-reported mortality, and ecosystem change.[2] Observed deaths of these dolphins could be under-reported because small vessels do not have observers, observers do not see the net constantly at all times, injured dolphins die after observation, and dead individuals are not always reported.[14]
Bycatch, in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juveniles of the target species. The term "bycatch" is also sometimes used for untargeted catch in other forms of animal harvesting or collecting. Non-marine species that are caught but regarded as generally "undesirable" are referred to as rough fish or coarse fish.
The common dolphin is the most abundant cetacean in the world, with a global population of about six million. Despite this fact and its vernacular name, the common dolphin is not thought of as the archetypal dolphin, with that distinction belonging to the bottlenose dolphin due to its popular appearances in aquaria and the media. However, the common dolphin is often depicted in Ancient Greek and Roman art and culture, most notably in a mural painted by the Greek Minoan civilization.
The false killer whale is a species of oceanic dolphin that is the only extant representative of the genus Pseudorca. It is found in oceans worldwide but mainly in tropical regions. It was first described in 1846 as a species of porpoise based on a skull, which was revised when the first carcasses were observed in 1861. The name "false killer whale" comes from having a skull similar to the orca, or killer whale.
The pygmy killer whale is a poorly known and rarely seen oceanic dolphin. It is the only species in the genus Feresa. It derives its common name from sharing some physical characteristics with the orca, also known as the killer whale. It is the smallest cetacean species that has the word "whale" in its common name. Although the species has been known to be extremely aggressive in captivity, this aggressive behavior has not been observed in the wild.
The Indo-Pacific bottlenose dolphin is a species of bottlenose dolphin. This dolphin grows to 2.6 m (8.5 ft) long, and weighs up to 230 kg (510 lb). It lives in the waters around India, northern Australia, South China, the Red Sea, and the eastern coast of Africa. Its back is dark grey and its belly is lighter grey or nearly white with grey spots.
The melon-headed whale, also known less commonly as the electra dolphin, little killer whale, or many-toothed blackfish, is a toothed whale of the oceanic dolphin family (Delphinidae). The common name is derived from the head shape. Melon-headed whales are widely distributed throughout deep tropical and subtropical waters worldwide, but they are rarely encountered at sea. They are found near shore mostly around oceanic islands, such as Hawaii, French Polynesia, and the Philippines.
The Atlantic spotted dolphin is a dolphin found in warm temperate and tropical waters of the Atlantic Ocean. Older members of the species have a very distinctive spotted coloration all over their bodies.
The common bottlenose dolphin or Atlantic bottlenose dolphin is one of three species of bottlenose dolphin in the genus Tursiops. The common bottlenose dolphin is a very familiar dolphin due to the wide exposure it receives in captivity in marine parks and dolphinariums, and in movies and television programs. Common bottlenose dolphins inhabit temperate and tropical oceans throughout the world, absent only from polar waters. While formerly known simply as the bottlenose dolphin, this term is now applied to the genus Tursiops as a whole. As considerable genetic variation has been described within this species, even between neighboring populations, many experts think additional species may be recognized.
The spinner dolphin is a small dolphin found in off-shore tropical waters around the world. It is famous for its acrobatic displays in which it rotates around its longitudinal axis as it leaps through the air. It is a member of the family Delphinidae of toothed whales.
The Clymene dolphin, in older texts known as the short-snouted spinner dolphin, is a dolphin endemic to the Atlantic Ocean. It is the only confirmed case of hybrid speciation in marine mammals, descending from the spinner dolphin and the striped dolphin.
The striped dolphin is a dolphin found in temperate and tropical waters of all the world's oceans. It is a member of the oceanic dolphin family, Delphinidae.
Cetacean bycatch is the accidental capture of non-target cetacean species such as dolphins, porpoises, and whales by fisheries. Bycatch can be caused by entanglement in fishing nets and lines, or direct capture by hooks or in trawl nets.
Dolphin-safe labels are used to denote compliance with laws or policies designed to minimize dolphin fatalities during fishing for tuna destined for canning.
The Inter-American Tropical Tuna Commission is a tuna regional fishery management organisation responsible for the conservation and management of tuna and other marine resources in the eastern Pacific Ocean.
William F. Perrin was an American biologist specializing in the fields of cetacean taxonomy, reproductive biology, and conservation biology. He is best known for his work documenting the unsustainable mortality of hundreds of thousands of dolphins per year in the tuna purse-seine fishery of the eastern tropical Pacific. This work became a primary motivation for the U.S. Marine Mammal Protection Act (1972). His work on cetacean taxonomy was acknowledged in 2002 when a newly recognized species of beaked whale, Perrin's beaked whale, which was named in his honor.
Cetaceans form an infra-order of marine mammals. In 2020, approximately 86 species of cetaceans had been identified worldwide. Among these species, at least 35 have been sighted in the wider Caribbean region with very widespread distribution and density variations between areas. Caribbean waters are a preferred breeding site for several species of mysticeti, who live further north the rest of the year. The tucuxi and the boto live at the southern periphery of the Caribbean region in the freshwaters of the Amazon River and surrounding drainage basins.
1 2 3 Perrin, William F. "Stenella attenuata." Mammalian species(2001): 1-8.
↑ Wade, P. R. "Revised estimates of incidental kill of dolphins(Delphinidae) by the purse-seine tuna fishery in the eastern Tropical Pacific, 1959-1972." Fishery Bulletin 93.2 (1995): 345-354
1 2 3 Gerrodette, Tim, and Jaume Forcada. "Non-recovery of two spotted and spinner dolphin populations in the eastern tropical Pacific Ocean." Marine Ecology Progress Series 291 (2005): 1-21.
↑ Perrin, William F. "Pantropical spotted dolphin: Stenella attenuata." Encyclopedia of Marine Mammals (Second Edition). 2009. 819-821.
↑ Kasuya, Toshio. "Japanese whaling and other cetacean fisheries (10 pp)." Environmental Science and Pollution Research-International 14.1 (2007): 39-48.
↑ "Appendix IIArchived 11 June 2011 at the Wayback Machine " of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). As amended by the Conference of the Parties in 1985, 1988, 1991, 1994, 1997, 1999, 2002, 2005 and 2008. Effective: 5 March 2009.
↑ Baur, DONALD C., MICHAEL J. Bean, and MICHAEL L. Gosliner. "The laws governing marine mammal conservation in the United States." Conservation and management of marine mammals. Smithsonian Institution Press, Washington, DC (1999): 48-86.
↑ Read, Andrew J., and Paul R. Wade. "Status of marine mammals in the United States." Conservation Biology 14.4 (2000): 929-940.
↑ Bayliff, W. H. "Organization, functions, and achievements of the Inter-American Tropical Tuna Commission (IATTC Special Report No. 13)." Retrieved form https://www.iattc.org/SpecialReportsENG.htm Google Scholar (2001).
↑ Reilly, STEPHEN B., and J. Barlow. "Rates of increase in dolphin population size." Fishery Bulletin 84.3 (1986): 527-533.
↑ Lennert-Cody, Cleridy E., Stephen T. Buckland, and FERNANDA FC MARqUES. "Trends in dolphin abundance estimated from fisheries data: a cautionary note." Journal of Cetacean Research and Management 3.3 (2001): 305-320.
Further reading
Pantropical Spotted Dolphin by William F. Perrin in Encyclopedia of Marine Mammals pp.865–867. ISBN978-0-12-551340-1
Whales Dolphins and Porpoises, Mark Carwardine, Dorling Kindersley Handbooks, ISBN0-7513-2781-6
National Audubon Society Guide to Marine Mammals of the World, Reeves, Stewart, Clapham and Powell, ISBN0-375-41141-0
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